Heavy syllable endings and the origin of Pre-PIE mobility

Proto-Indo-European featured a complex system of accentual and ablaut paradigms. In this paper, I outline a proposal for the development of accentual mobility in Pre-PIE. The accent-ablaut system is mostly described as a morphologically conditioned, but its diachronic origin is likely phonetic. Based on the behavior of the most archaic lexical and morphological layer, root nouns and verbs, I argue that ending morphemes with heavy syllables attracted stress, which results in accentual mobility. While the rule was not phonetically active in PIE, it leaves traces and allows us to explain some forms that were difficult to explain. The rule also provides a simple phonetic motivation for a complex morphophonological system of PIE accentual mobility.